1. Field of the Invention
Aspects of the present invention relate to a secondary battery having an electrolyte injection hole and a method of fabricating the same.
2. Description of the Related Art
In recent years, compact, lightweight, portable electronic/electric devices, such as cellular phones, notebook computers, and camcorders, have been actively developed and produced. Such devices include battery packs having rechargeable batteries, for portable operations. Examples of rechargeable (secondary) batteries include nickel-cadmium (Ni—Cd) batteries, nickel-metal hydride (Ni-MH) batteries, and lithium (Li) batteries.
Li secondary batteries are widely used in portable electronic devices, due to having an operating voltage that is three times higher than that of Ni—Cd batteries and Ni-MH batteries. In addition, Li secondary batteries have a higher energy density per unit weight. Li secondary batteries may be lithium ion batteries that include a liquid electrolyte, or lithium polymer batteries that include a polymer electrolyte. Li secondary batteries may also be cylindrical, prismatic, or pouch-shaped.
In general, a lithium secondary battery pack includes: a bare cell; a can to house the bare cell; and a protective circuit assembly electrically connected to the bare cell, to prevent the bare cell from being overcharged and/or over-discharged. The bare cell includes: an electrode assembly that includes; a can to house the electrode assembly; and a cap assembly to seal the can. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator disposed therebetween. The electrode plates each have a collector that is coated with an active material, and an electrode tab connected to the collector. The protective circuit assembly includes a protective circuit board for controlling voltage and/or current when the bare cell is charged and/or discharged. The battery pack can include: a lower case formed between the protective circuit board and the bare cell, to provide a space where the protective circuit board can be placed; and an upper case coupled to the lower case, to protect the protective circuit board from external impacts.
FIG. 1 is a cross-sectional view of a conventional secondary battery 10, including an electrolyte injection hole 26. Referring to FIG. 1, the secondary battery 10 includes a can 11, an electrode assembly 12 accommodated in the can 11, and a cap assembly 20 coupled to the can 11.
The electrode assembly 12 includes a positive electrode 13, a separator 14, and a negative electrode 15, which are wound together. A positive electrode tab 16 and a negative electrode tab 17 are drawn from the positive electrode 13 and the negative electrode 15, respectively. An insulating case 18 is provided on the electrode assembly 12, to electrically insulate the electrode assembly 12 from the cap assembly 20 and to cover an upper portion of the electrode assembly 12.
The cap assembly 20 includes a cap plate 21 coupled to an upper portion of the can 11, an electrode terminal 23 that is insulated from the cap plate 21 via a gasket 22, an insulating plate 24 provided on a lower surface of the cap plate 21, and a terminal plate 25 provided on a lower surface of the insulating plate 24, which is electrically connected to the electrode terminal 23.
The positive electrode tab 16 is electrically connected to the cap plate 21, and the negative electrode tab 17 is electrically connected to the electrode terminal 23, through the terminal plate 25. The cap plate 21 includes the electrolyte injection hole 26, which is a passage for injecting an electrolyte into the can 11. A sealing member 27 is coupled to the electrolyte injection hole 26, to seal the same.
The sealing member 27 is normally an aluminum ball that is pressed into the electrolyte injection hole 26, by a pressing device. After the ball is pressed into the electrolyte injection hole 26, laser welding is performed to form a welded portion 28, along a boundary between the ball and the cap plate 21. A UV activated hardener is coated around the periphery of the electrolyte injection hole 26 and on the sealing member 26, and is then cured by UV light.
However, it is difficult to properly position the ball in the electrolyte injection hole 26, due to the shape of the conventional electrolyte injection hole 26. This reduces the strength of the seal, which may result in leakage of the electrolyte from the can.
In addition, since an upper surface of the ball cannot be precisely rounded, the welded portion 28 may not be correctly formed, resulting in leakage of the electrolyte. In particular, when the electrolyte leaks through the conventional electrolyte injection hole 26, during the welding process, the leaked electrolyte causes a pin hole to be formed between the ball and an inner circumference of the electrolyte injection hole 26. This degrades the sealing characteristics of the electrolyte injection hole 26.